There are numerous well-known fluoropolymers in the class generally regarded as fluoroplastics, including both partially crystalline and amorphous fluoropolymers. Commonly, these polymers are stable at high temperature and resistant to chemical attack, with the degree of stability and inertness increasing with fluorine content in the molecule. While the chemical properties of known fluoropolymers are highly desirable for many purposes, their inertness also has the effect of making it difficult to produce solutions of the fluoropolymers or to bond other materials to them. When the polymer contains only perfluorinated monomers, the resultant perfluoropolymer is most difficult to put into solution.
Resnick in U.S. Pat. No. 3,978,030 describes certain polymers of perfluoro-2,2-dimethyl-1,3-dioxole (PDD), including both homopolymers of PDD, which are not further characterized, and a crystalline copolymer of tetrafluoroethylene (TFE), which has a melting point T.sub.m of about 265.degree. C. Since Resnick's discovery of PDD homopolymer, it has been established that the material is amorphous and has a very high glass transition temperature T.sub.g of about 335.degree. C. The homopolymer is brittle and difficult to fabricate into final products because of poor melt flow and low solubility in available solvents.
Squire in U.S. Pat. No. 4,530,569 describes amorphous dipolymers of PDD with TFE as well as terpolymers of PDD with TFE and another comonomer. In U.S. Pat. Nos. 4,935,477 and 4,754,009, Squire describes dipolymers and terpolymers (collectively, copolymers) of PDD with comonomers which include certain perfluoroolefins and perfluoro(alkyl vinyl) ethers. It is shown in these patents that, in general, the T.sub.g of those copolymers decreases with increasing comonomer content, although not necessarily in a linear fashion. For a dipolymer containing 10 mol % of TFE, T.sub.g is decreased to about 260.degree. C. Generally, if the PDD content of those copolymers is less than about 12 mol %, those copolymers have some crystallinity. While the amorphous copolymers are soluble at room temperature in perfluoro(2butyl tetrahydrofuran), their solubility is not high. For example, a dipolymer with 10 mol % of TFE has a solubility of less than 3 wt % in this solvent. This imposes some restrictions on fabrication techniques that require application of copolymer from solution, such as dip-coating or spray-coating.
U.S. Pat. No. 4,897,457 to Nakamura et al. describes homopolymers and copolymers containing 6-membered and 5-membered rings derived from the monomer CF.sub.2 .dbd.CF--OCF.sub.2 CF.sub.2 CF.dbd.CF.sub.2, perfluoro(butenyl vinyl ether) (PBVE) which forms the cyclic structure(s) during polymerization. For the amorphous homopolymer, T.sub.g is only about 108.degree. C. Comonomers disclosed have the effect of reducing T.sub.g. Moreover, it is stated that copolymers with fluorinated olefins and vinyl ethers lose transparency, solvent-solubility, and mechanical strength if repeat units derived from PBVE constitute less than 80 wt % of the polymer.
Hung in U.S. Pat. Nos. 4,982,009 and 5,059,720 discloses hydroxy-containing fluorovinyl ethers and polymers containing units derived from those ether monomers. Among those hydroxy-containing fluorovinyl ethers, a preferred monomer is CF.sub.2 .dbd.CFO--CF.sub.2 CF(CF.sub.3)O--CF.sub.2 CF.sub.2 --CH.sub.2 OH (EVE-OH).